transfection quality DNA- help

[apeel at maple.circa.ufl.edu]

Am having difficulty obtaining >40% supercoiled DNA with PBPR 322 vectors using
Qiagen columns for 500 ml cultures, even though a 1.5 sample of the same
culture run through a Qiagen minicolumn gives marvelous supercoiling.  Don't
have the same problem with vectors using pBS backbone.  Any ideas (the PBR
vectors are also quite larege 9 - 11kb- is this a factor?)  Don't get much
better results with Maniatas PEG purification and this is a much longer
procedure.  Am not set up to do CsCl centrifugation.  Suggestions, comments,
similar results with PBR 322 backbone vectors and these preps?